Lithium ion batteries (LIBs) are one of the most widely used portable power sources. However, loss of power and capacity upon storage or prolonged use especially at elevated temperature (>50° C.) limits the application of LIB for electric vehicle (EV) and hybrid electric vehicle (HEV) applications. The performance degradation is frequently linked to the thermal instability of lithium hexafluorophosphate and the reactions of the electrolyte with the surface of the electrode materials. This has prompted the development of alternative electrolytes for lithium ion batteries.
The most widely utilized lithium salt for lithium ion batteries is lithium hexafluorophosphate (LiPF6). However, LiPF6 has poor thermal and hydrolytic stability and is thus not ideal. One of the most widely investigated “alternative” salts for lithium ion battery electrolytes is lithium bisoxalatoborate (LiB(C2O4)2, LiBOB). Lithium ion batteries containing LiBOB based electrolytes have been reported to operate up to 70° C. with little capacity fade. However, the use of LiBOB has been limited by the poor solubility of LiBOB in common carbonate solvents and the poor performance of LiBOB electrolytes at low temperature. LiBOB based electrolytes have been reported to generate a stable solid electrolyte interface (SEI) on the surface of the anode due to ring-open reactions of the oxalate moiety and the formation of trigonal borates.